Transmissions (e.g., optical or radio-frequency waveforms) used in traditional free-space communications experience various reflections, for example due to physical structures or atmospheric variations, and cause multiple versions of the waveform to arrive at a receiver with varying time delays. If a line-of-sight path exists between the transmitter and the receiver, the direct line-of-sight signal will be the first to arrive at the receiver and will tend to be the strongest signal received, though such may not always be the case. Any of the delayed versions may be the strongest signal, depending upon conditions. “Multipath” is a general term for the phenomenon of multiple versions of the transmitted signal related to the multiple paths between the transmitter and the receiver. The reception of multipath signals may cause signal fading in traditional receivers. Rake receivers, however, process received signals in a manner to exploit the additional delayed versions of the most direct signal.
Conventional rake receivers for optical communications tend to be complex, requiring extensive processing in the optical domain, such as to accommodate differing polarization of the various multipath signals, and accordingly include significant optical components that have substantial spatial and alignment requirements and limit flexibility.